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Information about Dbms
Business & Mgmt

Published on March 15, 2014

Author: TejKiran2



  Problems with file processing systems  Inconsistent data  Inflexibility  Limited data sharing  Poor enforcement of standards  Excessive program maintenance

 Character :The most basic logical element is character.Which consists of alphabetic, numeric or other symbol. Field : It consists of grouping of characters.For example, the grouping of alphabetic characters.For example grouping of alphabetic characters in a person’s name form a name field. Record :Related fields of data are grouped to form a record. File :A group of related records is a data file, or table. Database :The highest level in the hierarchy is the database.A database is an integrated collection of logically related records or files. Levels of Data

  Controlled Redundancy  Ease of learning and use  Data independence  Accuracy and Integrity  Privacy and security  Shared  Recovery from failure  Performance Objectives of Data Base

  Operational Data Base  Analytical Data Base  Data Warehouse Data Base  Distributed Data Base  End User Data Base  External Data Base Types of Data Bases

  Data Bases store detailed data needed to support operations of entire organization  They are also called Subject Area Databases ,transaction database and production database  A customer database, inventory database, and other database containing data generated by business operations Operational Database

  Databases store data extracted from selected operational and external databases  Consists of data mostly needed by an organization’s managers and other end users  They are also called management databases or information databases  They are the databases accessed by the online analytical processing (OLAP) systems, decision support systems and executive information systems Analytical Database

  Stores data from current and previous years that has been extracted from various operational and analytical databases of an organization  It is a central source of data that has been standardized and integrated so it can be used by managers and other end user professionals throughout an organization Data Warehouse Databases

  Databases of local work groups and departments at regional offices, branch offices, manufacturing plants and other work sites  Can include segments of common operational and common user databases as well as data generated and used only at a user’s own site  Ensuring that all the data in distributed databases are consistently and concurrently updated Distributed Database

  These databases consist of a variety of data files developed by end users at their workstations  For example, users may have their own electronic copies of documents they generated with word processing packages or received by electronic mail. End User Database

  Access to external online databases or data banks is available for a fee from commercial information services , or for free of price from many sources on the internet  For example, data are available in the form of statistics on economic and demographic activity from statistical data banks  Abstracts from newspapers, magazines, and other periodicals from bibliographic data banks External Database

 DBMS is the software that permits an organization to centralize data, manage them efficiently, and provide access to the stored data by application programs . DBMS acts as an interface between the application program and the physical data files DBMS has three components  A data definition language  A data manipulation language  A data dictionary Database Management System

  The data definition language is the formal language used by the programmers to specify the content and structure of database  It defines each data element as it appears in the database before that data element is translated into the forms required by application programs Data Definition Language

  This language contains commands that permits end users and programmers to extract data from the database to satisfy information requests and develop applications  The most prominent data manipulation language today is structured query language (SQL) Data Manipulation Language

  This is an automated or manual file that stores definitions of data elements and data characteristics such as usage, physical representation, ownership, authorization and security  Many data dictionaries can produce lists and reports of data utilization, groupings, program location and so on Data Dictionary

  Organizes data  Integrates data  Separates data  Controls data  Retrieves data  Protects data Functions of DBMS

  Reduced programming costs  Reduced development and implementation time  Reduced program and file maintenance costs  Reduced data Redundancy  Increase flexibility Benefits of DBMS

 Data is not stored in a random fashion. It is organized for efficient retrieval.  Sequential organization  Indexed Sequential Organization  Inverted List Organization  Direct Access Organization Data Storage and Retrieval

  It simply means storing and sorting in physical, contiguous blocks within files on tape or disk  Records are also in sequence within each block  It is best suited in reading one record after another without a search delay  The records can be added only at the end of the file Sequential Organization

  Data is stored in physically contiguous blocks and uses indexes to locate records  Indexed Sequential Organization reduces the magnitude of the sequential search and provides quick access for sequential and direct processing  The drawback is the extra storage space required for the index. It also takes long to search the index for data access or retrieval Indexed Sequential Organization

  It differ from the previous in the index level and record storage  The indexed sequential method has a multiple index for a given key, whereas the inverted list method has a single index for each key type  In inverted list records are not needed to be stored in a particular sequence. They are placed in data storage area but indexes are updated for the record keys and location  Inverted lists are best for applications that request specific data on multiple keys Inverted List Organization

  In direct access file organization, records are placed randomly throughout the file  New records are added at the end of the file or inserted in specific locations based on software commands  Records are accessed by addresses that specify their disk locations. An address is required for locating a record, for linking records , or for establishing relationships Direct Access Organization

 Hierarchical Data Model Employee Job assignments BenefitsCompensation Performance Salary hist Pension Life insurance Health

 Network Data Model Course 2Course 1 Course 3 Student 1 Student 2 Student 3 Student 4 Student 5 Student 6

 Relational Data Model Dept .no D nam e D loc Em p no Dep. A Dep. B Dep. C Emp . no E name E title E sal Dep. no E1 D A E2 D A E3 D B E4 D B E5 D C E6 D A

  The schemes (schema) define categories of data and their properties .  External Schema or user schema is the user’s view of a part of the database  Conceptual Schema is the overall logical view of the database  Internal Schema or data storage definition is the way the data is physically organized in storage Data Schemes

 External Schemas General Model User View User View User View Conceptual Schema Internal Schema Stored Database

  Each user of the database (an application program or a person formulating a query ) is concerned with only a small portion of the database  Each user is interested in only a part of the entities in the database, only part of the attributes of those entities, and certain relationships among the entities  External schema consists basically of definitions of each of the various external record types in the external view  The external schema is written using the DDL portion of the user’s data sub language External Schema

  The conceptual schema is the logical view of the entire database . It represents as closely as possible the real entities and their relationships .  It contains integrity rules and authorization rules, but it does not contain information about how the data items are stored Conceptual Schema

  The internal schema or physical data model describes how the database is organized for physical storage and access  The internal schema includes information on ordering of records, block sizes, storage indexes, use of pointers and access strategies being used Internal Schema

  A mapping is a transaction of one schema to another  In order for a user to access data, the user view of the data as reflected in the external schema must be translated into the overall conceptual schema  In the same way, the conceptual/internal mapping translates logical descriptions of data in the conceptual schema to physical locations and access paths in the internal scheme Mapping

 Mapping between Schemas External view External view External view External schema1 External schema 2 External schema 3 Overall conceptual view Conceptual schema Internal schema (DDL) Stored Database

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